Fixed ``test_login_required``  when run without ``mezzanine.accounts``.

Note 1: Always testing both scenerios no matter what's in the settings
would be thorough, but without something like the 1.7+ ``modify_settings``
it turns out ugly. It would be better to run the whole suite with and
without some optional apps.

Note 2: This test passes when run through ``runtests``, but it cheats
by forcing ``mezzanine.accounts`` into installed apps ;-)